To limit the delivery of incoming messages in Qmail to the servers of EuropeanMX, please follow the steps below:
If you use Qmail in conjunction with tcpserver, you can add the following rule under etc/tcp.smtp so that all incoming connections are accepted by EuropeanMX.
=delivery.antispamcloud.com:allow,RELAYCLIENT=''
If you run Qmail as an inetd service using tcp-env, the entire configuration of SMTP access is done from the following files: /etc/hosts.allow and /etc/hosts.deny. Do not forget to add your own SMTP clients to /etc/hosts.allow.
Add the following line to file /etc/hosts.allow:
tcp-env: .antispamcloud.com: setenv = RELAYCLIENT
Add the following line to file /etc/hosts.deny:
tcp-env: ALL
This prevents all incoming connections except the one specified via the file in step 1.